class_docstr: **CNN / Daily Mail** 数据集的 **Loader** ，用于 **extractive summarization task** 任务。
  如果你使用了这个数据，请引用 https://arxiv.org/pdf/1506.03340.pdf
  
  读取的 :class:`~fastNLP.core.DataSet` 将具备以下的数据结构：
  
  .. csv-table::
     :header: "text", "summary", "label", "publication"
  
     "['I got new tires from them and... ','...']", "['The new tires...','...']", "[0, 1]", "cnndm"
     "['Don't waste your time.  We had two...','...']", "['Time is precious','...']", "[1]", "cnndm"
     "['...']", "['...']", "[]", "cnndm"
  
  :param fields:
docstr: 自动下载数据集。
  
  :return: 数据集目录地址
docstr_tok: ["\u81ea\u52a8\u4e0b\u8f7d\u6570\u636e\u96c6\u3002",":","return",":","\u6570\u636e\u96c6\u76ee\u5f55\u5730\u5740"]
code: def download(self):
      r"""
      自动下载数据集。
  
      :return: 数据集目录地址
      """
      output_dir = self._get_dataset_path("ext-cnndm")
      return output_dir
  
file_path: fastNLP/fastNLP/io/loader/summarization.py
imports: import os
  from typing import Union, Dict
  from ..data_bundle import DataBundle
  from ..utils import check_loader_paths
  from .json import JsonLoader
label_desc: Use image node_id 3 for calling the ExtCNNDMLoader obj's underlying member method code with example usage: obj.download() and returns: output_dir